If you are trying for the UFO Ending, this is the second place to use the Blue Gem. Use it on the dock next to the boat before boarding it.
Enter the row boat and cross Toluca Lake. Your final destination is the Lake View Hotel. Turn the boat to the right until you see a search light in the distance. Once you have it behind you, row toward it.
Rowing is done differently according to the difficulty setting you’re playing on:
Easy & Normal – Simply move the left analog stick in the direction you wish to go.
Hard – You will have to use both thumbsticks to mimic a rowing motion.
As with the on foot controls, holding the “run” button will make the boat move faster.
Complete this stage in less than 80 seconds to earn the Don’t Keep Her Waiting achievement / trophy.
After rowing long enough, a cut scene will occur. You’re now at the Lake View Hotel.